Interpretive Summary: Changing fire regimes and the increased use of prescribed fire in invasive species management implore improved understanding of fire effects on rangeland runoff and erosion processes. In this study, we applied artificial rainfall and overland flow to burned and unburned sagebrush rangelands to quantify runoff, infiltration, and erosion over a three year period. The greatest impact of fire was the removal of ground cover. The removal of vegetation and groundcover and the influence of naturally occurring strong soil water repellency increased the spatial connectivity of overland flow, reduced runoff and sediment filtering effects of ground cover, and increased overland flow velocity, volume, and sediment transport. The impacts of wildfire on runoff generation and sediment yield were greatly reduced after two growing seasons. The study provides a relative measure of the increased risk of runoff and erosion and the rate of hydrologic recovery following fire on steep coarse-textured sagebrush landscapes.

Technical Abstract:
Changing fire regimes and prescribed-fire use in invasive species management on rangelands require improved understanding of fire effects on runoff and erosion from steeply sloping sagebrush-steppe. Small (0•5 m2) and large (32•5 m2) plot rainfall simulations (85 mm h–1, 1 h) and concentrated flow methodologies were employed immediately following burning and 1 and 2 years post-fire to investigate infiltration, runoff and erosion from interrill (rainsplash, sheetwash) and rill (concentrated flow) processes on unburned and burned areas of a steeply sloped sagebrush site on coarse-textured soils. Soil water repellency and vegetation were assessed to infer relationships in soil and vegetation factors that influence runoff and erosion. Runoff and erosion from rainfall simulations and concentrated flow experiments increased immediately following burning. Runoff returned to near pre-burn levels and sediment yield was greatly reduced with ground cover recovery to 40 percent 1 year post-fire. Erosion remained above pre-burn levels on large rainfall simulation and concentrated flow plots until ground cover reached 60 percent two growing seasons post-fire. The greatest impact of the fire was the threefold reduction of ground cover. Removal of vegetation and ground cover and the influence of pre-existing strong soil-water repellency increased the spatial continuity of overland flow, reduced runoff and sediment filtering effects of vegetation and ground cover, and facilitated increased velocity and transport capacity of overland flow. Small plot rainfall simulations suggest ground cover recovery to 40 percent probably protected the site from low-return-interval storms, large plot rainfall and concentrated flow experiments indicate the site remained susceptible to elevated erosion rates during high-intensity or long duration events until ground cover levels reached 60 percent. The data demonstrate that the persistence of fire effects on steeply-sloped, sandy sagebrush sites depends on the time period required for ground cover to recover to near 60 percent and on the strength and persistence of ‘background’ or fire-induced soil water repellency.